If your server and client fully evidence the indicators as described
in the cited IC62348 APAR, you could pursue that.  Otherwise, pursue
applying the current maintenance level to your 5.5.0 client, which is
unhealthily running at base level, with no maintenance.  Once that is
done, if the problem persists, I would perform some isolation
testing, and turn on client tracing if that depth of information is
necessary.

   Richard Sims